The present invention relates generally to a medical device for treating tissue and methods of use, and more particularly, to a medical device and methods for radiofrequency thermal ablation which is provided with a controlled cooling means according to the Peltier effect for effectively creating a large lesion.
This invention relates to an electrode element assembly for treating a target tissue by providing thermal energy to the target tissue while simultaneously providing cryogenic energy to the peripheral tissue adjacent or surrounding the target tissue adapted for shielding the peripheral tissue from the effect of thermal therapy.
Generally, thermal energy could be clinically applied to treat tissue, such as tumor, cancerous tissue, prostate, arrhythmia, atrial fibrillation and the like. However, difficulties have been encountered for a device system to provide highly controlled, localized heat to a precise point or region within a patient""s body that causes little effects to the peripheral tissue adjacent, encircling, or surrounding the target tissue.
In a patient""s heart, supraventricular tachycardia, ventricular tachycardia, and atrial fibrillation are conditions collectively known as arrhythmias. During an arrhythmia, abnormal electrical signals are generated in about the endocardial tissue which cause irregular beating of the heart. One method used to treat these arrhythmias involves creating lesions within the chambers of the heart or the pulmonary veins. These lesions are intended to halt the passage of the abnormal currents through the heart. A radiofrequency catheter has been routinely used to ablate the aberrant electrical activity. Increasing the radiofrequency power to a catheter in an attempt to increase the size of the lesions has caused degradation of the blood in the region where ablation is taking place.
U.S. Pat. No. 5,348,554 to Imran et al. discloses a catheter system with a cooled electrode. Specifically, an electrode having a chamber therein is provided with a circulated cooling liquid to cool the electrode. U.S. Pat. No. 6,241,666 to Pomeranz et al., and U.S. Pat. No. 6,015,407 to Rieb et al. also disclose a catheter system with a modified cooled electrode, mostly with a liquid coolant arrangement that is bulky, expensive or poses unnecessary risk to a patient. The entire contents of the above-cited patents are incorporated herein by reference.
A radiofrequency catheter with a liquid-cooled electrode includes extra auxiliary equipments, such as a circulating pump, a cooling liquid source, control instruments, and accessories. As disclosed in U.S. Pat. No. 5,348,554, the cooled liquid is intended to cool the inner chamber of the tip electrode. However, the temperature of the outer surface of the electrode may rise to an unacceptable level resulting in tissue degradation, blood clot, or coagulation. As is well known to an ordinary technician skilled in the art that the resistive heat of radiofrequency ablation comes from the tissue-electrode contact surface. In an example of U.S. Pat. No. 5,348,554, a portion of the isotherm G showed in FIG. 18 is in the blood-contacting region. Even with a liquid-cooled setup thereof, the isotherm temperature of the isotherm G might reach as high as 66.633xc2x0 C. which is far above the cell necrosis temperature.
Therefore, there is an urgent clinical need for providing a medical device and methods for treating a target tissue comprising providing thermal energy to the target tissue and simultaneously or subsequently providing cryogenic energy to the peripheral tissue adjacent or surrounding the target tissue adapted for shielding the peripheral tissue from any detrimental effects of the thermal energy, if any.
Johnson et al. in U.S. Pat. No. 4,860,744 discloses a thermoelectrically controlled heat medical catheter, which is incorporated herein by reference. More particularly, Johnson et al. discloses a system and methods for providing controlled heating or cooling of a small region of body tissue to effectuate the removal of tumors and deposits, such as atheromatous plaque. Though Johnson et al. teaches a medical catheter in accordance with the Peltier effect adapted for thermoelectric heating/cooling for destruction of diseased tissue and/or tumors in various parts of the body, Johnson et al. does not disclose a method for cooling the peripheral tissue so as to focus the therapeutically thermal energy to the target tissue alone.
Larsen et al. in U.S. Pat. Nos. 5,529,067, 5,755,663, and 5,967,976 disclose methods and apparatus for use in procedures related to the electrophysiology of the heart, such as identifying or evaluating the electrical activity of the heart, diagnosing and/or treating conditions associated with the electrophysiology of the heart, entire contents of which are incorporated herein by reference. Specifically, Larsen et al. teaches an apparatus having thermocouple elements of different electromotive potential conductively connected at a junction and reducing the temperature of the junction in accordance with the Peltier effect for cooling the contacted heart tissue. However, Larsen et al. does not teach a method for treating a target tissue comprising providing thermal energy to the target tissue and simultaneously or subsequently providing cryogenic energy to the peripheral tissue adjacent or surrounding the target tissue adapted for shielding the peripheral tissue from any adverse effect of the thermal energy.
In general, it is an object of the present invention to provide a device and a method for treating a target tissue, the method comprising providing thermal energy to the target tissue and providing cryogenic energy to peripheral tissue adjacent or surrounding said target tissue adapted for shielding the peripheral tissue from any adverse effect of the thermal energy. The cryogenic energy provided for the peripheral tissue may be provided simultaneously, subsequently or in a pre-programmed mode with respect to the thermal therapy at no higher than 37xc2x0 C. and is compatible with the tissue viability or functionality.
In one embodiment, the method of cooling may be provided by a probe junction, the probe junction being conductively connected to two elements of different electromotive potential and electrical current being passed through the elements to reduce temperature of the probe junction in accordance with the Peltier effect and thereby cool the peripheral tissue adjacent or surrounding the target tissue.
In another embodiment, the target tissue may be selected from a group consisting of tumor, cancerous tissue, arrhythmia, pulmonary vein, benign prostate hyperplasia, breast tumor, breast cancer, inflammation, atherosclerosis, vulnerable plaque, or the like. The thermal energy may be selected from a group consisting of radiofrequency energy, microwave energy, laser energy, ultrasound energy, and combination thereof.
It is another object of the present invention to provide an electrode element assembly comprising a metallic tip electrode, means for delivering current to the metallic tip electrode, elements of different electromotive potential conductively connected at a probe junction, wherein the probe junction surrounds at least a portion of periphery of the metallic tip electrode, and means for passing an electrical current through said elements to reduce temperature of said probe junction in accordance with the Peltier effect.
In still another embodiment, the probe junction may form a complete circle or circular-like configuration that surrounds the periphery of the tip electrode. The probe junction may optionally be permeably porous for fluid or particles passage. The electrode assembly is configured so as the metallic tip electrode being adapted for intimately contacting the tissue to be treated and the probe junction being adapted for not contacting the tissue to be treated. The metallic tip electrode may further comprise at least a needle or probe configured for penetrating into the tissue to be treated.
It is still another object of the present invention to provide an apparatus for treating tissue comprising at least one electrode assembly, wherein said electrode assembly comprises a metallic tip electrode; means for delivering current to the metallic tip electrode; elements of different electromotive potential conductively connected at a probe junction, wherein the probe junction surrounds at least a portion of periphery of the metallic tip electrode; and means for passing an electrical current through said elements to reduce temperature of the probe junction in accordance with the Peltier effect and thereby cool tissue adjacent the treated tissue. The apparatus may be a catheter, a probe, a cannula, or an endoscopic instrument.